GNGTS 2013 - Atti del 32° Convegno Nazionale

Meduno windgap (Fig. 2), the river shifted towards the west deepening the valley of about 200 m. This change was tentatively correlated to the deformation phase well recognized in the foothills (Caputo et al. , 2010). The new Meduna valley crossed the Periadriatic thrust (PE in Fig. 1) whose activity may have driven the geomorphological change. In addition, the thick Q1 conglomerate, exceeding 40 m, suggests a local subsidence at the footwall of the Periadriatic thrust itself. 2. Calabrian (?). A second important deepening of the valley, of about 150 m, with a westward shifting, occurred between Q1 and Q2 aggradation phases. However, the lack of chronological data for these two units makes speculative the age attribution of this phase. It is likely that a tectonic uplift drove this deepening, but it needs more investigations. 3. Calabrian-Middle Pleistocene. This event is recognizable at the boundary between Q2 and Q3 units. Here the Q2 conglomeratic unit presents a crude bedding, gentle folding (dip ca. 10-15°, from 340° to 45°). The Q2 unit is unconformable cut by another conglomerate (Q3) horizontally bedded. Both can be ascribed to alluvial sedimentation of the Meduna Stream within a valley reach, while the angular unconformity suggests a relative time-span occurred between their deposition. Moreover, Q4 is related to a glacial advance during the late Calabrian – middle Pleistocene (Fig. 2), suggesting a similar age for the deformation. An angular unconformity ascribed to the same time span is visible in the conglomerate succession of the Tagliamento valley (Monegato and Stefani, 2011). 4. Middle-upper Pleistocene-Holocene. This tectonic event involves both the M. Jouf thrust and the Maniago one, showing a clear shifting of the tectonic activity from the inner thrust (M. Jouf th.) to the external one (Maniago th.). It is the better constrained tectonic event. On the terrace near Meduno, the Q5 unit (Middle Pleistocene, upper portion, Fig. 2) give rise a transition from “strath terrace” located in the hangingwall of the M. Jouf thrust to “fill terrace” in the footwall of the thrust. Therefore according to Wegman and Pazzaglia (2009) a broad tectonic control on the formation of this terrace can be hypothesized. Moreover, Q1 unit (Del Bianco conglomerate, probably Early Pleistocene in age) is crosscut by the M. Jouf thrust. Here the conglomerate is strongly fractured and tilted back of about 20°. Fig. 3 – NW-SE geological profile across the LGM terrace on left side of Meduna Stream near Ponte Maraldi. Q6: Ponte di Pietra sedimentary unit (upper Pleistocene); Q7: Sequals syntem (Travesio lobe, upper Pleistocene – 22-23 ka cal. BP); Q8: Sequals syntem (Arba lobe upper Pleistocene-Holocene). TRZ: Tarzo Marl (Lower Serravallian- Lower Tortonian); VVE: (Vittorio Veneto Sandstone, Tortonian); MON1 and MON2: Montello Conglomerate members (Upper Tortonian-Lower Messinian). 196 GNGTS 2013 S essione 1.2